Wood products are generally classified according to the thickness of the wood. Wood products two inches thick and greater, e.g., a two-by-four, are classified as lumber. Wood products less than two inches thick but greater than one inch thick, e.g., a one-by-six, are classified as boards. Veneer sheets or slats are those wood products that are less than one inch thick. (It is noted that a two inch thick piece of lumber has an actual finished thickness of one and one-half inches, while a one inch thick board has an actual finished thickness of three-quarter inches.)
Because of the uses for, processing of, and structure of these classes of wood products, they are generally viewed as separate industries. Additionally, it has generally been observed that methods for processing lumber or boards may not be technically possible or economically feasible when processing veneer, and vice versa. For example, prior attempts to compress the moisture out of lumber have been unsuccessful. Lumber dried by prior compression techniques results in damaged pieces that are not usable.
Cutting veneer from timber occurs primarily by one of two techniques; rotary cutting and slice cutting. Rotary cut veneer is cut from a rotating log by applying a cutting edge to the log so that layers of the log are removed. Slice cutting veneer involves slicing a log from one end through its longitudinal axis to its second end. The number of slats or sheets that may be taken from a piece of timber depends on the width of each piece of veneer. In the veneer industry, the thickness of veneer is expressed in the number of slats to the inch. For example, "ten to the inch," is ten slats each 0.1 inch thick.
Veneer must be dried following cutting to lower its moisture content before it can be used. A freshly cut piece of veneer may have a moisture content as high as 90%. The moisture content of a usable piece of veneer should be below 30%.
A previously developed method for drying veneer may include placing the veneer in a kiln or drying oven. Typically, veneer pieces are laid flat on a conveyor or rack system within the drying oven. Alternatively, the veneer pieces may be fed through a series of rollers that are both above and below the veneer in the oven. The rollers hold the veneer flat while it is being dried in the oven. Heat draws the moisture out of the veneer. Drying veneer in this manner can be a very difficult process. If the veneer is dried too quickly or at too high a temperature, moisture in the veneer will turn to steam that may damage the cell structure of the veneer. Veneer with a damaged cell structure lacks the strength necessary to be useful.
Previously developed methods for drying veneer may require extensive time in order to dry the veneer. It is not uncommon for these prior methods to require at least 30 minutes to dry the veneer. The cost of heating the oven, as well as the labor to load and unload the oven, add to the veneer's cost.
Another prior method for drying veneer includes placing the veneer pieces between heated plates and then applying heat and pressure to the veneer. Unfortunately, this method suffers from all the disadvantages of any heat drying technique. It is difficult to control, slow, expensive, and labor intensive.
Compression techniques for squeezing out the moisture in veneer have been previously developed. These previous methods involve compressing a veneer slat with a compressive force generated by two sets of rollers turning at different speeds along the length of the slat. This technique can damage the veneer and cause it to buckle. Additionally, it may not remove sufficient moisture and often requires additional heat drying.